In order to prevent data dependent average signal power, quadrature amplitude modulation (QAM) requires scrambling of the data bits to produce a uniformly distributed signal set. More particularly, by constantly sending the same constellation point during QAM modulation, an accurate representation of the average transmit power for the constellation cannot be obtained. This results in an inability to accurately determine the constellation point. For example, without data scrambling, a frame consisting of all 0's will result in the same transmitted QAM symbol. Such data dependent average signal power adversely affects signal peak-to-average power, which in turn degrades receiver AGC performance. This effect is especially pronounced for a single user occupying multiple Walsh code channels in the 1X evolution (EV), data and voice (DV) system.
A prior-art 1XEV-DV system 100 is shown in FIG. 1. As is evident, long-code scrambling takes place after QAM modulation. As such, long code scrambler 103 scrambles modulation symbols 102 with the long code samples at the modulation symbol rate. This results in symbol phase rotation only. As a result, when the data is constant (i.e. all 0's) the transmitted QAM symbols will all have the same energy (radius). Therefore, a need exists for a method and apparatus for data transmission that mitigates the constant transmission of a same radius during QAM modulation.